Monday 28 November 2011 16.00 EST
First published on Monday 28 November 2011 16.00 EST

I'm moving through the lobby of one of Los Angeles' whimsy-luxe hotels on my way to meet actor Joseph Gordon-Levitt in a penthouse suite. Surrealist flourishes abound: chairs in the shapes of lips and twigs, and full-size horse statues that double as lamps. The overall effect is African ski lodge meets Mad Men, glazed with a dollop of melting clock. The setting is fitting, given Gordon-Levitt's eclectic career. He has morphed from the androgynous alien kid in long-running 90s TV hit Third Rock from the Sun to the teen gay hustler in Gregg Araki's 2004 film Mysterious Skin, bouncing on through characters as varied as (500) Days of Summer's lovelorn romeo, Hesher's charismatically violent burnout, and Inception's corporate dream-fiddling crook.

Gordon-Levitt's current cinematic volte-face is as a cancer-stricken everydude named Adam in the weepy but unexpectedly funny 50/50. Adam is an idealistic radio producer whose shock diagnosis uncomfortably highlights the shortcomings of everyone in his life, including his own. Girlfriend Rachael (Bryce Dallas Howard) is a poseur artist whose wooden attempts to care for her newly-sick boyfriend misfire wincingly. While Adam's overbearing mother (Anjelica Huston) tries to muscle back into his life with equal measures of comedy and pathos, he becomes a guinea pig for his rookie therapist Katherine (Anna Kendrick), whose inexperience mirrors his in the scary new world they're negotiating together.

Not only is the story based on screenwriter Will Reiser's real-life battle with a rare spinal tumour (discovered while he was a producer on Da Ali G Show), but Reiser's real-life best friend, Seth Rogen, plays Adam's best friend. Rogen gives a charmingly bombastic performance as the party-hearty boob who only wants to lighten his buddy's worries. But it's Gordon-Levitt's low-key progression from initial bewilderment at his predicament to taking control of his life – even as it potentially slips away – that quietly anchors the movie. That, and his signature crinkly-twinkly smile.

There's no crinkly-twinkling on display by the time I shake hands with Gordon-Levitt ("JGL" in PR patois). Lanky and sliver-slim, the 30-year-old flickers between weary and wary as he settles into a sofa. His slicked-back hair and neatly sculpted sideburns suggest "reformed juvie", a look reinforced by his chambray denim shirt, jeans and black loafers. Windshield-wiper eyebrows are the animated parentheses on a face whose delicate puppet features suggest an odd yet appealing blend of Gene Kelly and Marky Mark.

He eyes me suspiciously when I ask what music he'd played earlier to gear up for the day. After some hesitation, he answers: "I was listening to Sam Cooke and the Soul Stirrers – it's very good morning music."

"Did you find yourself singing along, shaking a tail feather?" I enquire, thinking of his joyfully corny Hall & Oates dance number in (500) Days of Summer. There's a pause while he regards me inscrutably. He cracks his knuckles in the silence. "Sure," he answers, his delivery dripping in "whatever". This is not an actor who relishes the interview process. Maybe I need to stick to the script. I quiz him on his sudden replacement of James McAvoy in 50/50, who had dropped out after the start of production because of a family emergency.

"The scariest part for them was there were a couple days where they didn't know if their movie was going to have to shut down," he says in a light, crisp speaking voice with the unplaceable refinement of a 40s radio performer. "A movie takes such a long time to put together and plan, and once it's in production, if something like that happens it's a nightmare. Seth called me in dire straits and asked if I would look at this script, and I was a fan of his so I did. We made friends really quickly, he and I – and Evan [Goldberg], his writing partner, and Jonathan Levine, the director, and Will, the screenwriter. We all just became very quick buds – [it's] a very brotherly, familial vibe that they get going."

Did he have to overcome expectations created by the few scenes McAvoy had already shot? "Hardly, and that's a credit to the director and everyone that they didn't make me feel that way, because it could've easily felt that way."

"James would've done it this way!" I tease.

"Yeah, there was none of that," he responds. "They had shot for four days with him …"

"Can you just have a look at the dailies and see what James came up with?" I'm cracking myself up, and JGL plays along by shooting me half a crinkly twinkle. Did I mention that his dimples are the animated quotation marks in his delicate puppet face? That's a lot of punctuation for one puppet.

"Definitely none of that," JGL repeats, firmly. "But I do remember once we got past the fourth day, I was like, OK, now I've done more than James had done."

Once he'd marked his territory on the 50/50 set, JGL didn't have a problem getting up to speed. After all, between writer and co-star, he was working with the original source material. "I didn't have to worry if what I was doing made sense, because Will was there," he explains. "And especially doing something that's sensitive like playing a guy with cancer. Having him there was crucial. And it wasn't like I was playing Will. I didn't walk and talk like him. It was much more taking the emotional story of his experiences [rather] than the empirical details of his actual personality, mannerisms, voice."

The head-shaving scene depicted on the poster was done in one take – by necessity. "You can't shave your head twice. No bald wigs. Shooting it, we rolled two cameras and we had to just do it. It's fun that way because a fundamental part of the movie-making process is that you can do it again. A big part of film acting is repetition, but with this scene, it becomes something almost theatrical – and that's exhilarating."

With all the theatrics, I venture, isn't it about time for a turn on Glee? All the popular kids are doing it – even Gwyneth Paltrow. This triggers an uncomfortable silence in which JGL regards me stonily, then bursts out laughing. I guess that's a no. But there's copious evidence on YouTube of his fine singing voice and obvious relish for performing. Many of the video clips are part of a website called HitRECord.org, JGL's pet project. HitRECord is billed as an "open-collaborative production company", where writers, musicians, animators and filmmakers build on-going digital mashups using each other's work. Born of a frustrated urge to express himself, HitRECord evolved into a way for JGL to share the joys of creativity with people who don't necessarily have his industry access. And these days, "people" number more than 50,000 members who share in the profits of any work to which they contribute. Think of it as a collective farm for artists, with JGL as Stalin. Or at least, "the benevolent dictator", as he refers to himself.

"At the very outset [HitRECord] was me in my early 20s, figuring out that as much as I love acting, playing roles conceived by other people wasn't all I wanted to do with my life," he says, his reserve thawing as he warms to a favourite subject. "I knew I wanted to make things, whether it was cinematic stuff or music or writing. I grew up with video cameras, making little videos. 'Hit record' became this personal mantra. That red circle became a symbol to me – pushing that button."

The move from child star to adult actor – and from TV to film – is notoriously tricky, which makes JGL's deft career transition in every area all the more impressive. "I'm sure luck has a lot to do with it, I wouldn't deny that," he allows. "For a while, after [Third Rock From the Sun] no one wanted to hire me to do anything but a TV show, and I didn't really want to do that again. I'm grateful to a few filmmakers who took a chance on me, like Gregg Araki, who made Mysterious Skin, or Rian Johnson, who made Brick. These are guys who were able to see that I could play these other roles. I really owe them all my subsequent opportunities."

At 19, JGL got a taste of civilian life when he attended Columbia University. "I wanted to not know what I was going to do with my life. I'd been acting since I was six, but all my friends where heading off to college and they had all these open possibilities and I wanted that. I thought, maybe I'll become a physicist, or maybe I'll ... whatever ..." He trails off, not sounding very convinced by the "open possibilities". In any event, the world was denied its first ever child-actor-turned-physicist when JGL treated himself to computer editing software for his 21st birthday. "I dropped out. It sort of happened when I got Final Cut Pro. I said to myself, well, I could be writing this paper, or I could be cutting a video. And the choice became pretty clear."

Did he at least leave Columbia with some book-learning under his belt? "I read a bunch of books – some history, some science," he confirms. "I learned French pretty well. I suffer from Francophilia. I think that's partly from movies and partly ... French girls are just really sexy to me."

JGL is currently shooting The Dark Knight Rises, Christopher Nolan's next instalment in the Batman epic. He plays a beat cop gunning to nab the Caped Crusader, another role that plots a wayward dot on his non-linear graph. But even with all the cinematic zigs and zags, we've yet to be treated to JGL in a British costume drama. He giggles at the absurdity when I suggest it.

How's his Cockney accent? "I tend to bleed into Aussie a lot," he confesses. "I have a few Australian friends, so that's my problem. One day I'd love to do it. I think I'd do it well, if I properly studied it."